Recently, a more general method is suggested to obtain critical exponents in Ref. [1]}. However, in our case, it is convenient to use method in Ref. [2]}. Now following method in Ref. [2]}, we can obtain critical exponents of phase transition for RN-AdS black hole. We cannot obtain the exact critical point due to the complexity of equation of state in Eq. (REF ) so we cannot obtain the law of corresponding states from Eq. (REF ) the critical exponent may differ from Ref. [2]}. On the other hand, we can compute the critical exponents for small thermal fluctuations. In the presence of small thermal fluctuations, we can obtain specific heat at constant volume, \(C_{V}=-a+\mathcal {O}(a^{2})\)  and this is independent of \(T\)  so exponent \(\alpha =0\) . Defining
\(p=\frac{P}{P_{c}},\quad \tau =\frac{T}{T_{c}},\quad \nu =\frac{V}{V_{c}}\, ,\) 
